An X-ray CT apparatus, which provides information on an object as images based on the intensity of X-rays having transmitted through the object, plays an important role in many medical practices including diagnosis and treatment of diseases and surgical planning.
Recent X-ray CT apparatuses use a technique known as dual energy scan. The dual energy scan as referred to herein is a technique for acquiring images by scanning an object using two different types of tube voltages. CT which uses dual energy scan is referred to as “dual energy CT.”
Techniques related to the dual energy scan have been known. These techniques can separate materials on the basis of information acquired using two different types of tube voltages, and then acquire various images, such as monochromatic X-ray images (monochromatic images), density images, effective atomic number images, and artifact-free images (images with reduced artifacts). The X-rays used for dual energy scan are polychromatic X-rays (continuous spectrum X-rays) having various X-ray energies and a specific X-ray energy distribution.
Furthermore, techniques have been known that generate two types of polychromatic X-ray images (polychromatic images) that are typical CT images corresponding to respective two types of X-ray energy distributions, and blend both the images, thus generating a monochromatic X-ray image taken at an X-ray energy desired by an operator.
In the monochromatic X-ray images taken at the required X-ray energy through dual energy scanning, beam hardening artifacts are reduced. Unfortunately, the monochromatic X-ray images have a problem of having higher noise than conventional polychromatic X-ray images taken in an X-ray energy band.
In actuality, the conventional polychromatic X-ray images taken at the X-ray energy band have reduced noise. However, these images have a problem in that beam hardening artifacts are difficult to be reduced in comparison with the monochromatic X-ray images.